now we have a table core.migration and each model (User, Group, Item, ItemContent and a new Migration) have its own
row in the table with a version number
added to config:
db_make_migration_if_needed and db_stop_if_migration_fails (need description yet)
- User and Group has been moved to 'models' directory
- removed UserPass struct (passwords fields were put to User struct)
not working yet, we need support for binary blobs in morm